In general, a hydraulic excavator which is a typical example of a construction machine is made hybrid by being provided with the two types of power sources, that is, an engine and an assist power generator/electric motor for assisting driving of the engine in order to promote improvement of fuel efficiency, purification of an exhaust gas and the like.
In this hydraulic excavator, a vehicle body is constituted by an automotive lower traveling structure and an upper revolving structure provided rotatably on the lower traveling structure. A working mechanism driven by a hydraulic actuator is provided on a front side of the upper revolving structure.
The upper revolving structure includes a revolving frame forming a support structural body, an engine provided on the revolving frame at a location on a rear part side of the revolving frame, a hydraulic pump driven by the engine and supplying a pressurized oil to the hydraulic actuator, an assist power generator/electric motor connected to the engine and the hydraulic pump performing a power generator action and an electric motor action, a cooling fan sucking an outside air as cooling air and supplying the cooling air to the engine by rotating with the engine as a power source, a heat exchanger provided on the revolving frame at a location closer to an upstream side in a flow direction of the cooling air than the cooling fan and cooling a fluid by the cooling air, and an electric power storage device disposed on the revolving frame at a location closer to the upstream side in the flow direction of the cooling air than the heat exchanger and charging generated power by the assist power generator/electric motor or discharging the charged power (Patent Document 1).